This invention is concerned with laser instruments as often used in construction. In particular, the invention addresses the problem of calibration for correct alignment of level or plumb beams or combinations of level, plumb and square beams in a laser instrument.
Multidirectional construction lasers produce visible reference beams of laser light at precise angles relative to each other and to the level and plumb directions. Such tools, including the LeveLite.RTM. manufactured by LeveLite Technology Inc. of Mountain View, Calif., are used widely by many construction trades such as dry wall installation, air conditioning installation, foundation layout, plumbing and many others. Conveniently aligning these beams during manufacture and while servicing is difficult because of the high angle accuracy required and the large space required in conventional methods of alignment. For example, a level beam is often calibrated using reference marks or monuments along a premeasured course. See FIG. 1, where monuments A and B are at level or a known height above level. The distances between the beam and height reference marks on the monuments are measured to align the beam to level. A distance of about 20 to 30 meters between the monuments is necessary for high accuracy. In a like manner a vertical beam may be aligned using two reference marks or targets sufficiently above the beam projector as shown in FIG. 2. A translucent target 20 to 30 meters above the projector is sufficient. In the simplest case the beam origin can be placed over a mark on the floor while the beam on the target above is marked as the point A. The projector can then be rotated 180 degrees about the beam origin and the beam location can be marked B. Because the direction of gravity is unchanged, the location of true plumb is half way between points A and B. The projector can then be calibrated by adjusting the beam so that the beam lies on the true plumb point.
The subject invention makes the alignment of a multi-directional reference lasers convenient and accurate by using lenses and a video sensor to compress the size of the measurement course from 30 meters to a matter of centimeters. Using mirror reflection, the resulting instrument can be used to align level, square and plumb beams simultaneously.